Field of the Invention
The present invention relates to a fuel cell stack, and a method of determining maintenance time of the fuel cell stack.
Description of Related Art
A fuel cell stack that is mounted on a vehicle includes a fuel cell stacked body (hereinafter, simply referred to as “stacked body”) and end plates (for example, refer to Japanese Unexamined Patent Application, First Publication No. H8-315846 (hereinafter, referred to as Patent Document 1)).
The stacked body is constituted by a plurality of unit cells which are stacked. Each of the unit cells includes a membrane-electrode assembly (hereinafter, simply referred to as MEA) having a configuration in which a solid polymer electrolyte membrane is interposed between an anode electrode and a cathode electrode, and separators which sandwich the MEA.
The end plates sandwich the stacked body from both sides in a stacking direction of the unit cells. The end plates are fastened to each other with the stacked body interposed therebetween. Accordingly, a fastening load acts on the unit cells along the stacking direction.
In the above-described fuel cell stack, a hydrogen gas is supplied to the anode electrode as fuel gas, and air is supplied to the cathode electrode as oxidant gas. According to this, a hydrogen ion, which occurs in the anode electrode due to a catalytic reaction, is transmitted through the solid polymer electrolyte membrane and moves to the cathode electrode. In the cathode electrode, the hydrogen ion causes an electrochemical reaction with oxygen in air, and thus power generation is carried out.
In the fuel cell stack, the fastening load, which acts on the unit cells, decreases depending on deterioration (for example, mechanical deterioration or chemical deterioration of the MEA, and the like) of the stacked body. When the fastening load decreases, for example, contact resistance between the unit cells (between separators of adjacent unit cells) increases, and a resistance overvoltage increases. According to this, extraction efficiency of electric power that is generated in the unit cells decreases, and power generation performance deteriorates. In addition, sealing properties between the unit cells deteriorate, and thus there is a concern that leakage of a reaction gas and the like may occur.
Accordingly, for example, Patent Document 1 discloses a configuration in which a decrease in a load, which acts on unit cells, is determined by measuring a voltage drop between two constituent components (for example, a cooling plate and an air electrode) between which the solid polymer electrolyte membrane is not interposed. According to this configuration, the voltage drop increases due to an increase in contact resistance between constituent components in accordance with a decrease in a load, and thus it is considered that the decrease in the load can be determined.